Thermionic energy detector



April 15, 1947. v H. I. BECKER 9, 5

THERMIONIC ENERGY DETECTOR Filed Sept. so. 1943 Inventor":

' HowardLBecker; by z wmw w HisAttorn ey.

Patented Apr. 15, 1947 THERMIONIC ENERGY DETECTOR 1 I Howard I. Becker, Rcxford, N. "Y.,"assignorto General Electric Company, a'corporation of New York Application September 30,1943, serial No. 504,485

My invention relates to thermionic energy detectors and, particularly, to electronic systems andapparatus for measuring the intensity and,

if desired, the frequency of pulsating thermionic radiant energy, such as for example the infra-red radiation which is emitted from the exhaust of A, an internal combustion engine, or through the propeller of an approaching aircraft, or the like.

It is a principal object of my invention to provide a new and improved electronic apparatus for detecting pulsating or periodic thermal ,transfer.

The invention isparticularly concerned with thermionic radiation measurement, and has for ,a particular object the provision of means for increasing substantially the response of electronic detecting apparatus for such radiation beyond the response of such apparatus heretofore known.

. Thev particular features of novelty characteristic of my invention will be pointed out with .particularity in the claims appended hereto. The

invention may be more fully understood, however,

' and itsobj ects and advantages further appreciated byreferring now to the following detailed specification taken in conjunction with the accompahying drawings, in which Fig. 1 is a schematic circuit diagram of a thermionic radiant energy detecting apparatus embodying my invention; Fig. 2 is a schematic circuit diagram of another such apparatus embodying my invention in modified form; and Fig. 3 is a graphical representation of the thermal characteristic of the detecting electric discharge device.

Referring now to the drawings, I have shown "at Fig. 1 an electric discharge device locomprising a thermal sensitive electron emitting cathode ;l I positioned between a pair of anodes I2. The

electrodes II and I2 are enclosed within a suitable evacuated envelope which may be of glass or metal and provided with a suitable window I 3 through which thermal-radiant energy, such as I infra-red rays, may be directed toward the cathode I I.

Preferably, such a window is composed of a fusible inorganic salt, such as a halogen salt of sodium or potassium or calcium fluoride. As' disclosed in Patent 2,125,113, granted to A. K.

Klingon July 26, 1938, such a window maybe inexpensively constructed of rock salt.

, The cathode I l is positioned directly in the path of radiant energy entering the rock salt window I3 in the evacuated envelope. Preferably, ine cathode is formed of a flat ribbon of thoriated 'tungs'te'n or a fiat ribbon of tungsten coated with a suitable oxide for increasing the electron emis 55 6 Claims. (01. 250 833) 2 I sivity of its surface. Oxides suitable for this pur pose are barium oxide, caesium oxide, and the likel Preferably, the anodes I2 comprise fiat metalli'c'fplates which may be semi-circular in shape and disposed so on opposite sides of the cathode "II that the planes of the anodes I2 are positioned at a slight angle with respect to each other. f

I have shown at Fig. 1 the anodes I2 electrically connected together and to one terminalof a'primarywinding I5 of a transformer I6. The

opposite terminal of the primary winding I5 is connected tofa' suitable source of positive potentialfs uch'as a battery IT. The cathode. I I'of the electric discharge tube Ill'is also connected to the battery I l ata'point negative with respect to thepoint ofbonnectibn of the transformer ,wind in'g' I5, thereby "to; complete an output or load circuit for the discharge device III.

'connected'tobe heated by current from the bat- Thecathode of the discharge device I0 is tery I'l througha circuit comprising a variable resistor 18, a tertiary winding I Son a transformer '20, and'the cathode II, all connected'in series circuit relationjbetween points of'suitable potential difference on the battery I'i.

The transformer I6 is provided also with a secondary winding 2| shunted by a tuning capacitor 2| a and having one terminal connected to a control grid 22 of a low frequency electronic amplifying device 23. The amplifier 23 comprises also an anode 24 and a cathode'25. The anode 24 is connected to one terminal of a primary winding 26 on the transformer 20, the opposite terminal of which is connected to a suitable source of positive potential on the battery I1.

1 The cathode 25 of the amplifier 23is also connected to the battery I! at a point more negative in potential than the pointto which, the primar'yfwinding 26 of the transformer 20 is connected. The transformer winding 2 I, which supplies the input power for the amplifier, 23 and has oneterminal connected to the control grid 22, also has its other jterminal connected to a point von the battery-ll whichis more negative .in potential than; the'point to which the cathode 25 is connected,-'thereby normally to bias the amplifier 23 negatively. The cathode'25 is heated by current from points of suitable potential difference on the battery I! through a circuit including a variableresistor 21.

The transformer'n is provided also with a secondary winding 28 connected to a suitable measuring-pr indicating device 29, such as an ammeaiaoca ter, voltmeter, cathode ray tube, loudspeaker, or the like,

The thermal electron emission characteristic of the electric discharge device lil may be represented by a curve such as the curve A of Fig. 3. This curve represents the relation between plate current, Ip, and cathode temperature, .Tc. "It-will be notedthat at some intermediate point, such as B, in the range of temperature values, the

rate of change of plate current with temperature is a maximum.

tween the anode and cathodeeofitheldischar e device Ill and the electric.discharge device-lwis directed so that pulsating thermal radiant energy from a source the temperature or distance of which is to be measured'falls'upon thec'athode II, a plate current flows havingsansinstantaneous value proportional to the instantaneous temperature of the cathode 1 The temperature of the cathode Lisdetermind byJthe sum lofthe heating .efiects of the received radiant energyland ;the electric heating'circuit. Preferably; the var- .;iable resistor. |8 .is. so. adjusted that the' average .cathode temperature. resulting from the sum, of nthe currenth'eating and the radiant energy-heating falls somewhere near the pointB onthejc'urve -..A of Fig... 3. Thus; as the cathode temperature is, periodically .increaSedL and decreased instanstaneously. by the pulsation of the receivedradiant energy, the. anode current pulsates and an Laltern'ating component 7 of current at'ithe fre- Zq'uency ,of i the radiant "energy" pulsation 'fio'ws lfthrough the transformer l6. The alternating poatentials thus. n-inducedhiniithe 'seconda'ry winding 1'2 ..of the transformer l 6 Z are amplified in the .l discharge i device 23 Iand applied to the output transformer 20. These amplified' o'scillations appear Lupon'l the secondary "iivinding" '28 f of the L transfo'rmer"2||v and are applied to the indicating mt measuring device 29.

IQFor. the purpose of in'creasi'ngthe sensitivity of ;v. fny' detecting. apparatus to lradi'atedfithermionic lcen'ergygl .provide for regenerativefeedback of energy from the output 'trarisformerf zfl 'tolthe r cathode heating circuit of 'theldi's'clfar'ge-device 1 0. It is forlthislpurpose ithat'th tertiary winding 3 of the. output transformer-i 20- is connected ...in, series circuit relation in the heating circuit LIfOr the cathode I. of the-rdischargefdevicefiUjjTo Qfensure regeneration," rather than l degeneration, l fromfthe-windingl9, itlis only necessary to so arrange the circuits that the oscillations appear- Hingvacr'oss the windingl9- are .in phase with the radiant' .energy pulsations received by the oathode'l Lof the discharge device I 0. To fuftherien- .sure' maximum response, it willbe- 'clearth'at'the tuning condenser Zla should be adjusted so that 'fthe parallel resonant circuit comprisingthe "(transformer winding 2| and thdcondenser' 2|a "is tuned to'the frequency of the receivedradiant energy pulsations. v

'Atiig; 2, I haveshown-anotherembodiment of my invention in which the-electric discharge device I is provided with abontrDlgrid and a "suppressor-grid between the cathode l and each bf the-anodes l2. The control grids arePeI'ectri- ="-'cally connected together and are identified=by the '1' reference numeral--30. :The suppressorigrids-are ra'alsorelectrically connected together and are: identified by the referencewnumeral -3l. Furthercmore, as at Fig. 1; theanodesll are electrically aconnected together and to. one terminal of a aprimary winding332 mi -a1 transformer--33 -.'Ihe

opposite terminal of the primary winding 32 of s 4 i the transformer 33 is connected to a point of positive potential upon a battery 34, while the cathode II is directly connected to a point on the battery 34 which is relatively negative in potential. Furthermore, between points of suitable potential difference upon the battery 34, is

.- connected a cathode heating circuit including a lvariableresistor 35 andthe cathode llconnected in series circuit relation. The suppressor grids l0 '3| are connected directly to a suitable point upon the battery 34 positive with respect to cathode potential; in -order that the discharge device Ill l-Inay be properly biased, the control grids 30 are vconnectedthrough a tertiary winding 36 on the transformer; 33 to a suitable point upon the battery 34 which is slightly more negative in poten- -tial'than-the'point to which the cathode H is connected. The unidirectional potential applied from the battery 34 to the control grids 30 through the tertiary winding 36 provides a negative bias for the" discharge device I 0.

.JIhe. transformer 33 is provided withasecondary winding. 31 having connected'in' parallel'circuit relation therewith'a tuning capacitor 38. The secondary winding: 3H is connected to the input of .an amplifying electric discharge device "39 having an anodeMLacathode 4|; and a con- Ztrol electrode42. The anode isconnected to one. terminal of a primary winding -430f an'outiput transformer. The'other terminal'of the winding 43 is connected to" a suitable source of positive potential, such as a battery45. 'The cathode 4| ,of the discharge "device 39 'is con- 'nected to a suitable point 'oftnegative potential ,upon the battery '4'5,'-and a cathode heating cir- "cuit for the cathode 4| is connected-through a "variableresistor' lfi between points of suitable potential"differenceupon the battery 45. Finally, thettransformer winding 31 has one terminal 40T'C'O'I1Il60t6d't0 "the control grid 42'of the amplifier '39 and theother'terminal connected to a-point on the battery '45 which isslightIymQre'negatiVe 1 in' potentialthan the point of' connection to the cathode 4|. The'section of the battery 45*be- 45jtween the cathode 4| and the connected termi- "nal' of the transformer-winding 3l-jprovides a "source of negative" bias potential for the control gridAZ. The amplified signal'upon the transformer winding is applied'to a suitable measuring or indicating device througha secondary. winding 48 upon the output transformer 44. In the operation of the apparatus'of Fig. 2;the cathode heating circuit of theelectric'dis'charEe device 0 is adjusted in the "samemanner as described heretofore in connection with Fig. 1. Thus; when pulsating infrared-radiation falls ".upon the. cathode l l, the anode'currentin the :"electriddischarge device 'lil varies periodically thereby to provide an alternating component of o'current'inthe transformer-'33. "The signal thus "induced in the transformer "33 is amplified inthe idischarge device39' and impressed upon the inl'di'cating' device 41 through the 'transformer '44. Simultaneously; also, an alternating potential at ".[the frequency ofthe received pulses "of thermionic :energy'is induced in the tertiary winding35 of the :transformer 33." The potentialiinduc'ed'in the ter- "tiary winding 36 is connected'in' series circuit re- .lation in the control grid bia'singj circuit for the electric discharge device 10; whereby this alterv ating potential is'superposed upon the normal unidirectional bias. potential of the .control grid 1130.; '.The alternating potential on the'winding 36 v, rv-willtbe substantially in phase withthe pulsations 7 of thermionic energy'towhichthe'cathodel| is .upon the cathode II, the tertiary winding 36 instantaneously raises the potential of the control grid 30 in a positive direction, thereby further to increase the anode current and to enhance the response of the apparatus to the radiated thermionic pulsations.

While I have shown only certain preferred embodiments of my invention by way of illustration, many further modifications will occur to those skilled in the art and I, therefore, wish to have it understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A thermionic radiant energy detecting apparatus comprising an electric discharge device having an anode and a thermo-sensitive electron emissive cathode, electric heating means for said cathode comprising a source of unidirectional potential, means for exposing said cathode to pulsating thermal radiant energy, said cathode controlling the anode current of said discharge device in accordance with instantaneous variations in intensity of said pulsating radiant energy, and means connected in series circuit relation between said cathode and said source of unidirectional potential for deriving from said anode current an alternating potential of like frequency and time phase relation with the pulsations of said radiant energy, thereby regeneratively to increase the response of said discharge device to said radiant energy.

2. A thermionic radiant energy detecting apparatus comprising an electric discharge device having an anode and a thermo-sensitive electron emissive cathode, electric heating means for said cathode connected in circuit with a source of unidirectional potential, means for exposing said cathode to pulsating thermal radiant energy, said cathode establishing electric oscillations in the output of said discharge device in accordance with variations in instantaneous intensity of said pulsating radiant ener y, means including a transformer for amplifying said electric oscillations, and a winding inductively associated with said transformer and connected in series circuit relation between said cathode and said source of unidirectional potential for deriving from said output circuit and applying to said cathode heating circuit an alternating potential in aiding time phase relation with the pulsations of said radiant energy, thereby regeneratively to increase the response of said discharge device to said radiant energy.

3. A thermionic radiant energy detecting apparatus comprising an electric discharge device having an anode, a control electrode and a thermosensitive electron emissive cathode, means for exposing said cathode to pulsating thermal radiant energy to control the anode current of said device in accordance with the instantaneous thermal energy level of said cathode, and means for deriving from said anode current and applying to said control electrode a potential in'aiding time phase relation with said pulsating radiant energy for increasing the response of said anode current to aid radiant energy.

ing through said window.

4. A thermionic radiant energy detecting apparatuscomprising an electric discharge device having an anode, a control electrode and a thermoresponsive electron emissive cathode, means for exposing said cathode to periodically pulsating thermal radiant energy, means including a transformer responsive to the anode current of said discharge device for detecting the intensity of said radiant energy, a winding on said transformer for deriving a potential of like time phase relation with said periodic pulsations of radiant energy, and means for applying said potential to said control electrode regeneratively to increase the response 'of said electric discharge device to said radiant energy.

5. A thermionic radiant energy detecting apparatus comprising an electric discharge device having an anode, a control electrode and a thermoresponsive electron emissive cathode, a source of negative bias potential connected in circuit between said cathode and said control electrode, means for exposing said cathode to periodically pulsating thermal radiant energy, means including a transformer responsive to the anode current of said device for detecting the intensity of said radiant energy, a tertiary winding on said transformer for deriving a potential of like time phase relation with said periodic pulsations of radiant energy, and means for superposing said derived potential upon said grid bias circuit in opposing relation to said negative bias potential regeneratively to increase the response of said electric discharge device to said radiant energy. I

6. Apparatus for detecting and measuring the intensity of pulsating heat energy waves comprising an electric. discharge device enclosed in an evacuated envelope having a window composed of a fusible inorganic salt, said discharge device having a two-part anode and a thermal responsive cathode, a source of electric energy for heating said cathode to a substantially constant temperature level, said cathode being positioned within said discharge device between the two parts of the anode'and opposite said salt window so as to have its temperature level varied by heat waves entering through said Window, means connected to said discharge device and responsive to the output thereof for detecting variations of the temperature level of said cathode, mean for deriving from the output circuit of said discharge device a potential proportional to such variations, and means for applying said derived potential to the discharge device in adding time phase relation with said variations thereby to increase the response of said device to variations in the heat Waves enter- HOWARD I. BECKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS" Number Name Date 1,343,393 Hoffman June 15, 1920 1,736,993 Breisky Nov. 26, 1929 1,744,192 Zowrykin Jan. 21, 1930 1,938,184 Kwartin Dec. 5, 1933 2,144,519 Wilson Jan. 17, 1939 2,204,053 Urtel June 11, 1940 

